32,866 research outputs found
Non-steady relaxation and critical exponents at the depinning transition
We study the non-steady relaxation of a driven one-dimensional elastic
interface at the depinning transition by extensive numerical simulations
concurrently implemented on graphics processing units (GPUs). We compute the
time-dependent velocity and roughness as the interface relaxes from a flat
initial configuration at the thermodynamic random-manifold critical force.
Above a first, non-universal microscopic time-regime, we find a non-trivial
long crossover towards the non-steady macroscopic critical regime. This
"mesoscopic" time-regime is robust under changes of the microscopic disorder
including its random-bond or random-field character, and can be fairly
described as power-law corrections to the asymptotic scaling forms yielding the
true critical exponents. In order to avoid fitting effective exponents with a
systematic bias we implement a practical criterion of consistency and perform
large-scale (L~2^{25}) simulations for the non-steady dynamics of the continuum
displacement quenched Edwards Wilkinson equation, getting accurate and
consistent depinning exponents for this class: \beta = 0.245 \pm 0.006, z =
1.433 \pm 0.007, \zeta=1.250 \pm 0.005 and \nu=1.333 \pm 0.007. Our study may
explain numerical discrepancies (as large as 30% for the velocity exponent
\beta) found in the literature. It might also be relevant for the analysis of
experimental protocols with driven interfaces keeping a long-term memory of the
initial condition.Comment: Published version (including erratum). Codes and Supplemental
Material available at https://bitbucket.org/ezeferrero/qe
Type Ia supernova Hubble diagram with near-infrared and optical observations
We main goal of this paper is to test whether the NIR peak magnitudes of SNe
Ia could be accurately estimated with only a single observation obtained close
to maximum light, provided the time of B band maximum and the optical stretch
parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H
photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183,
doubling the leverage of the current SN Ia NIR Hubble diagram and the number of
SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and
458 optical light curves (LCs) of normal SNe Ia from the literature. The
analysis of 45 well-sampled NIR LCs shows that a single template accurately
describes them if its time axis is stretched with the optical stretch
parameter. This allows us to estimate the NIR peak magnitudes even with one
observation obtained within 10 days from B-band maximum. We find that the NIR
Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first
time we report a possible dependence on the J_max-H_max color. The intrinsic
NIR luminosity scatter of SNe Ia is estimated to be around 0.10 mag, which is
smaller than what can be derived for a similarly heterogeneous sample at
optical wavelengths. In conclusion, we find that SNe Ia are at least as good
standard candles in the NIR as in the optical. We showed that it is feasible to
extended the NIR SN Ia Hubble diagram to z=0.2 with very modest sampling of the
NIR LCs, if complemented by well-sampled optical LCs. Our results suggest that
the most efficient way to extend the NIR Hubble diagram to high redshift would
be to obtain a single observation close to the NIR maximum. (abridged)Comment: 39 pages, 15 figures, accepted by A&
Soft Null Hypotheses: A Case Study of Image Enhancement Detection in Brain Lesions
This work is motivated by a study of a population of multiple sclerosis (MS)
patients using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI)
to identify active brain lesions. At each visit, a contrast agent is
administered intravenously to a subject and a series of images is acquired to
reveal the location and activity of MS lesions within the brain. Our goal is to
identify and quantify lesion enhancement location at the subject level and
lesion enhancement patterns at the population level. With this example, we aim
to address the difficult problem of transforming a qualitative scientific null
hypothesis, such as "this voxel does not enhance", to a well-defined and
numerically testable null hypothesis based on existing data. We call the
procedure "soft null hypothesis" testing as opposed to the standard "hard null
hypothesis" testing. This problem is fundamentally different from: 1) testing
when a quantitative null hypothesis is given; 2) clustering using a mixture
distribution; or 3) identifying a reasonable threshold with a parametric null
assumption. We analyze a total of 20 subjects scanned at 63 visits (~30Gb), the
largest population of such clinical brain images
Deep CFHT Y-band imaging of VVDS-F22 field: I. data products and photometric redshifts
We present our deep -band imaging data of a two square degree field within
the F22 region of the VIMOS VLT Deep Survey. The observations were conducted
using the WIRCam instrument mounted at the Canada--France--Hawaii Telescope
(CFHT). The total on-sky time was 9 hours, distributed uniformly over 18 tiles.
The scientific goals of the project are to select faint quasar candidates at
redshift , and constrain the photometric redshifts for quasars and
galaxies. In this paper, we present the observation and the image reduction, as
well as the photometric redshifts that we derived by combining our -band
data with the CFHTLenS optical data and UKIDSS DXS
near-infrared data. With -band image as reference total 80,000
galaxies are detected in the final mosaic down to -band point
source limiting depth of 22.86 mag. Compared with the 3500 spectroscopic
redshifts, our photometric redshifts for galaxies with and
mag have a small systematic offset of
, 1 scatter ,
and less than 4.0% of catastrophic failures. We also compare to the CFHTLenS
photometric redshifts, and find that ours are more reliable at
because of the inclusion of the near-infrared bands. In particular, including
the -band data can improve the accuracy at because the
location of the 4000\AA-break is better constrained. The -band images, the
multi-band photometry catalog and the photometric redshifts are released at
\url{http://astro.pku.edu.cn/astro/data/DYI.html}.Comment: 16 pages, 12 figures, 4 tables. AJ accepted. Updated access to the
data: https://zenodo.org/record/140003
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